Rasmus Benestad concluded in his 5 August RealClimate post Storms and Global Warming II that "there is little evidence of a trend in the [Tropical cyclone] frequency, [but ] there are some indications of a trend in the destructive capability of the TCs".

So there could be more category five storms in future. Given its potentially high impact, Hurricane Katrina may concentrate more minds on whether it is...cost effective to go along with those who deny the scientific consensus on climate change.

Meanwhile the scenes from New Orleans push a number of emblematic buttons: the conduit for one third of US domestic oil production shut down; Interstate 10, which was converted on Saturday so that all lanes headed one-way out of town, in total gridlock; and a substantial proportion of the Louisiana National Guard is off in...Iraq.

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King: Global warming may be to blameBy Andrew Buncombe The Independent31 August 2005

Sir David King, the British Government's chief scientific adviser, has warned that global warming may be responsible for the devastation reaped by Hurricane Katrina.

"The increased intensity of hurricanes is associated with global warming," Professor King told Channel 4 News yesterday. "We have known since 1987 the intensity of hurricanes is related to surface sea temperature and we know that, over the last 15 to 20 years, surface sea temperatures in these regions have increased by half a degree centigrade.

"So it is easy to conclude that the increased intensity of hurricanes is associated with global warming."

Professor Kerry Emanuel of the Massachusetts Institute of Technology also claimed, less than a month ago, that ocean surfaces had become warmer, which doubled the destructive potential of tropical storms in the past 30 years.

But he said that Monday's storm "is part of a natural" cycle of powerful Atlantic storms that have struck since 1995. He told The Independent: "I don't think you can put this down to global warming."

Other scientists point out that the 150-year record of Atlantic storms show there is ample precedent for hurricanes of Katrina's power. They say it is part of a natural upswing that has taken place since the mid-90s.

Officials at the US National Oceanic and Atmospheric Administration said records showed hurricane activity in the Atlantic had been higher than normal in nine of the past 11 years. This month the federal agency raised its hurricane forecast for this year from 18 to 21 tropical storms, including as many as 11 that would become hurricanes.

If that prediction holds true, it would make this year one of the most violent hurricane seasons recorded. A typical year in the Atlantic results in six hurricanes. The agency said the increase was likely to be the result of cyclical ocean and atmospheric conditions that produced heightened storms every 20 to 30 years.

William Gray, a Colorado State University meteorologist who is considered one of the fathers of modern tropical cyclone science, said worldwide weather records were too inadequate for a thorough examination of trends.

He told The Los Angeles Times: "The people who have a bias in favour of the argument that humans are making the globe warmer will push any data that suggests humans are making hurricanes worse, but it just isn't so ... These are natural cycles."